There is an expression in China: "Kill the chicken before the monkey." Target the weak and vulnerable, it means, to frighten the strong and many.

Last week, it was the turn of writer Zhao Shiying, secretary-general of the Independent Chinese Pen Centre, which campaigns on behalf of imprisoned writers and in favour of free expression.

Zhao was a signatory – along with Liu Xiaobo, a leading dissident jailed for 11 years on Christmas Day – of Charter 08, a document that called for political reform of China's state institutions. Police went to his home in the southern city of Shenzhen, near Hong Kong, on Monday to take him away, along with his computers, books and other documents.

It was his second visit from the police. In December, they had turned up and warned him not to cause trouble; the same threat was delivered to his wife, Shi Xiaoli, and adult son after his arrest. And while Shi had been warned not to talk of his detention, on Friday she defied them. "He's with state security agents," she said. "He's never been taken away for this long."

It is not only Zhao who has come under pressure for campaigning for the release of Liu Xiaobo. Since Liu's sentencing for "subverting the state" in organising Charter 08, China's authorities appear to have been engaged in an escalating campaign against activists and human rights groups that – say the groups – suddenly seems in danger of rupturing the country's fragile consensus permitting a degree of limited dissent short of political organisation that challenged the one-party status quo.

Instead, in the past year, Chinese authorities have been increasing pressure on well-known dissidents, which in recent months – according to Amnesty International – has seen them being "detained by the fistful".

The past week alone has seen not only Zhao's arrest, but also the revelation by Google that Chinese hackers, widely believed to be acting on the orders of the state, had targeted – not for the first time – the email accounts of human rights activists, including one belonging to Tenzin Seldon, a 20-year-old US ­student whose parents are Tibetan exiles. Most seriously, it also saw the announcement by the authorities that Gao Zhisheng, a prominent human-rights lawyer detained for 11 months, had "disappeared" while on a walk, prompting fears from his supporters he may have died in custody.

All of which raises an urgent question: why is China, the emerging superpower, so frightened of dissent?

It is a question that was asked earlier this month in an essay by historian Ian Buruma looking at why a regime, communist in name only and apparently so strong, is also so paranoid.

Buruma's answer is that the Chinese Communist party's insistence on orthodoxy can only be understood in cultural and historical terms, including what he describes as the "religious concept of politics… a shared belief imposed from above" that echoes the Confucian notion of harmony. Others see it, however, less in historical terms but as a reaction to what has been happening inside China today.

A former political aide to general-secretary Zhao Ziyang, Bao has spent seven years in jail and remains under house arrest. "Tiananmen is still here," he said then. "However, it's not a Tiananmen massacre; it's suppression in the style of a 'little Tiananmen'. Every four minutes there is a protest of more than 100 people."

They are protests about every social issue: about government corruption; land evictions; environmental contamination; police brutality; and schools. Diffuse and often disorganised, they represent, however, an increasingly vibrant grassroots scene, including such groups as the "rights defence movement" and personified by figures such as Gao Zhisheng, or fellow lawyer Guo Feixiong, imprisoned for representing villagers in Taishi, Guangdong province, who wanted to remove local officials accused of corruption.

It has also been visible in recent large-scale environmental protests involving demonstrations and "collective walks" on issues ranging from the siting of pharmaceutical factories to the routing of a train-line in Shanghai.

But what the Chinese Communist party fears most, according to human-rights activists and analysts, is that dissidents in the country's intelligentsia might act not only as a lightning rod for a myriad of social concerns by challenging the legitimacy of the state's institutions, but that they might provide an organisation to rally behind.

It is not an entirely new concern. It was this that drove Deng Xiaoping to order martial law in 1989 against the protesting students in Tiananmen Square and has also driven the persecution of the Falun Gong religious sect after it organised its own silent demonstrations at the end of the 1990s.

But what constitutes "organised" – and thus threatening to the state – has in the past year become ever more finely defined to include even Liu Xiaobo's internet petition that was Charter 08.

Corinna-Barbara Francis, a China expert for Amnesty International, describes the often miscalculated efforts by Chinese dissidents to keep on the right side of the regime.

"There are lines in the sand that people understand. Liu Xiaobo tried to keep just on the right side of them but Charter 08 pushed him over. But even then the sentence they gave him came as a shock."

The Chinese authorities chose to interpret the Charter 08 petition not simply as a critical statement but as evidence of "organisation" against the state. "It is why," said Francis, "China has really been upping the ante in the last year."

Liu's supporters expected him to get three years at most, but his sentence of 11 years in Beijing's Detention Centre Number 1 is on a par with those handed out to members of the Democratic party of China, founded in 1998, who have been hammered by the regime for forming an alternative political party.

But why Liu, 54, has been so harshly treated – and the scope of the authorities' fear of the internet – is revealed in the verdict handed out by Beijing Municipality First Intermediate People's Court. There, described in the bureaucratic language of oppression, are the Chinese Communist party's anxieties: collusion, organisation against the party and the propagation outside of the country's borders of a narrative critical of China.

"Between September and December 2008," the verdict reads, "the defendant Liu Xiaobo colluded with others to draft and concoct the 'Charter 08', that proposed views such as 'eliminate the monopoly of one party on the exercise of political power', 'to create a Chinese federation under the framework of democratic constitutional system of governance', seeking to incite the overthrow of state power. Liu Xiaobo had collected the signatures of more than 300 people and sent 'Charter 08' together with the signatures in an email to websites outside of the borders of mainland China, to publish it on websites outside the borders of mainland China such as 'Democratic China' and 'The Independent Chinese PEN Association'."

"The Communist party has had a monopoly on power for the last 60 years," said Phelim Kine, a researcher with the New York-based Human Rights Watch. "Everything it does is dedicated to holding on to power. The party has monitored and learned the lessons of the fall of the Soviet Union and the colour revolutions and is determined not to go down the same route. They have seen the necessity of controlling the narrative within their own borders. But they have also realised that they cannot be like North Korea and shut the country off. So they have created a paradigm where the party controls, but provides a level of economic development and economic rights. The price is the control of freedom of expression and other human rights."

And while many Chinese have accepted this trade-off, expressing bafflement at what they see as the west's obsession with a handful of dissidents, for a Chinese Communist party that has long thrown off most aspects of socialist ideology in favour of economic liberalisation the perceived threat of dissent has not diminished but increased.

One reason, some analysts believe, is that by largely dispensing with a guiding Marxist ideology that conferred values and moral meaning – by its own standards at least – on the party's institutions, those same institutions have become vulnerable to a line of criticism that questions what legitimacy they now claim.

The result, according to those like Bao Tong, is that there is less freedom now to criticise party leaders than there was in 1989, despite the fact that there exists, even within the party's own senior cadres, so-called "dangnei minzhupai", advocates for greater political liberalisation who crucially confine their political discourse to within the party.

And if there were a difference between the 1989 democracy movement and Charter 08, whose three principal drafters came out of that movement, it is this. While the events around Tiananmen created mass protests, they did not see the emergence of a document of coherent political demands. In comparison, the drafters of Charter 08, as historian Feng Chongyi noted in an essay in the Asia-Pacific Journal, pointedly embraced open democracy, while signalling their rejection of the one-party dictatorship – the most serious of heresies.

Kine believes that the imprisonment of Liu, and the increasing pursuit of his supporters, marks a convergence of multiple issues that have scared the Communist party: from Charter 08's use of the internet to Liu's emergence – in their eyes – as a leader of dissent by way of organising his petition.

"The Communist party is evolutionary and adaptive. It is no longer shooting people in the streets. It persecutes [figures such as Liu Xiaobo] to frighten dissenters and the nascent middle classes," Kine said.

And while Kine believes that China would probably have preferred that its hacking of Google accounts of human rights activists remained undiscovered, its disclosure by the internet giant serves a similar function as Liu's trial – forcing lawyers and bloggers and other activists to rethink how they communicate with one another.

Increasingly, it is the same threat that the authorities are using against those it has decreed have crossed the "invisible line" regarding freedom of expression and dissent – the charge of "subverting the state".

Another to have been imprisoned like Liu for "inciting subversion of state power" is Hu Jia, who led protests against deforestation in northern China before becoming a rights activist. Hu was sentenced on the same charges to three and a half years in prison in 2008.

Subversion, as understood by the regime these days, says Amnesty's Corinna-Barbara Francis, is "anything that makes people question the monopoly on power of the party. Despite economic successes, the party is steadfastly opposed to political reforms. It wants to keep the party in power and not share power with anyone.

"And what the elites fear now is what they feared in 1989: that intellectuals might inspire a wider mass dissent against the party."